1. Field of the Invention
The present invention relates to a vehicle cabin lighting apparatus for lighting the interior of a vehicle cabin of a vehicle to allow an imaging device installed in the vehicle cabin to capture an image of a subject, such as a vehicle driver, in the vehicle cabin.
2. Description of the Related Art
Heretofore, there has been known a vehicular imaging device for capturing an image of a vehicle occupant such as a vehicle driver in the cabin of a vehicle or a person approaching the vehicle, with an imaging device that is installed in the vehicle cabin, and processing the captured image to automatically detect an action of the vehicle occupant or features of the approaching person.
If the area surrounding a subject to be imaged by the imaging device is too dark, then the imaging device fails to capture a clear image of the subject. To solve this problem, the imaging device is combined with a lighting unit for illuminating the subject. When the lighting unit is energized, it emits illuminating light to illuminate the subject, which is made bright enough to be reliably imaged by the imaging device. For details, reference should be made to Japanese laid-open patent publication No. 2002-352229, for example.
The above publication shows a plurality of lighting units that are energizable in synchronism with imaging operation of the imaging device. A subject to be imaged is illuminated by the lighting units, and an image of the subject which is captured by the imaging device is processed for the user to accurately recognize a desired area of the subject. However, the intensities of illuminating lights emitted from the respective lighting units are constant at all times. If the subject changes its orientation with respect to the imaging device, e.g., if the face of a vehicle occupant to be imaged changes its orientation with respect to the imaging device, then shadows are created on the subject by the illuminating light, and the imaging device fails to capture a clear image of the subject because of the shadows.
If the subject changes its position, particularly, its distance to the lighting units, e.g., if the position of a vehicle occupant to be imaged which is seated on a seat in the vehicle cabin is changed, then the subject may not be illuminated with an adequate amount of illuminating light. For example, the illuminating light from the lighting units may be too intensive on the subject, tending to develop halation in the captured image of the subject. Alternatively, the illuminating light from the lighting units may be too weak, making the captured image of the subject dark and failing to detect a behavior of the subject from the processed image of the subject.